Emotional regulation partly determines individuals' adaptation to physical and psychological stressors; pain included. Previous work shows that an anger expressive style (anger-out) may be related to high pain sensitivity via dysfunction in the endogenous opioid system. Crucial elements of this biopsychological relationship remain to be explored. Two studies will use an experimental model to examine effects of anger-out on responses to painful stimuli. They will test whether: 1) arousal of anger is necessary for full expression of endogenous opioid differences linked to trait anger-out; 2) the opioid system dysfunction related to high trait anger-out is influenced by actual (behavioral) expressions of anger during anger arousal. Study 1 subjects will randomly receive either placebo or opioid blockade (naltrexone) prior to undergoing tasks. They will undergo a computerized maze task with harassment (anger induction) followed by an ischemic pain task, or will undergo tasks in reverse order. Significant Anger-Out x Task Order x Drug interactions are expected to show that high anger-outs have greater pain sensitivity due to endogenous opioid pain regulatory dysfunction, and that this dysfunction is most prominent when anger is induced prior to pain. Study 2 subjects will be screened for High/Low trait anger-out, and will randomly receive either placebo or naltrexone prior to undergoing tasks. All subjects will undergo the maze task with harassment, with instructions to either suppress or overtly express anger aroused during the task; an ischemic pain task follows. Significant Anger-Out x Drug x Express/Suppress interactions are expected such that high anger-outs will have greater pain sensitivity due to opioid regulatory dysfunction, but that behavioral anger expression in high anger-outs will trigger opioid system activation to dampen effects of anger arousal. This project will complement and expand research about the neurohumoral substrates of emotional regulation, and will enhance understanding of the interplay of anger regulation and endogenous opioids in the modulation of stress and pain. [unreadable] [unreadable]